Due to the limited availability and expense of natural leathers, numerous composite sheet materials have been developed to simulate the appearance and physical properties of natural leathers. Such synthetic leather products find wide commercial use as a substitute for natural leathers in manufacture of various products, such as garments, shoes, pocketbooks, and other wearing apparel and accessories.
U.S. Pat. No. 4,017,656 discloses an imitation leather material stated to be for use as shoe uppers which comprises a woven fabric having a napped face impregnated with a nitrile-butadiene resin to provide a flesh leather-like surface, and an unnapped face coated with a foamed polymer layer or layers, the outer surface of which is coated with a thin urethane resin layer which may be embossed to provide a leather appearance thereto.
U.S. Pat. No. 3,865,622 discloses a water-proof and oil-proof synthetic leather product for use in wearing apparel wherein a fabric such as a cotton woven fabric, is coated with a butadiene-acrylonitrile composition containing suitable pigments, clay thickening agents, and a curing agent.
U.S. Pat. No. 3,906,131 discloses a synthetic chamois leather like material comprising a non-woven textile fabric treated with a binder and coated on opposed faces with a coagulatable butadiene-acrylonitrile latex which may be mechanically foamed and applied to the non-woven fabric to form a porous layer.
B. F. Goodrich Chemical Co. Customer Service Report entitled "Chamois-Like Hycar Acrylate and Nitrile Latex Stand-Up Foams" dated Nov. 7, 1977 by Peter D. Seletzky discloses development work utilizing several acrylate and nitrile latex foam compositions to coat napped cotton and nylon fabrics to produce simulated chamois fabrics for use in manufacture of garments.
Of the many natural leather products, natural chamois leather has long been recognized as an excellent wiping cloth for cleaning, polishing and drying various surfaces, such as automobile bodies, and the like. Because of the soft, pliant, porous nature of the leather, natural chamois has a high rate of water absorption and a high level of water retention. When wet out, natural chamois is non-abrasive to surfaces on which it is used. From a standpoint of commercial acceptance and saleability, it is therefore desirable that any so-called synthetic leather wiping cloth products closely resemble the appearance, feel, and drape of natural chamois leather which the public has come to recognize as a standard of quality. From a performance standpoint, it is also desirable that such wiping cloth products have a fast rate of liquid absorption, typically of about five seconds or less (as measured by AATCC Test Method 79-1972), and an ability to retain absorbed liquid in an amount which is at least about 300 percent of the dry weight of the wiping cloth product. Although a number of so-called synthetic chamois wiping cloth products presently in the marketplace provide acceptable water retention for surface wiping operations, most are either rather stiff and broadly, have relatively low water absorption rates, or do not possess the appearance of natural chamois leather.
In this regard, it has been found that certain soft acrylonitrile polymers having relatively low glass transition temperatures, when applied as foam layers to opposed napped faces of a reinforcing textile fabric, provide excellent water-absorptive composite materials which very closely resemble the surface appearance, softness and drape of natural chamois leather. However, the attempted use of such soft polymers in the commercial manufacture of synthetic chamois leather wiping cloths presents many problems because of the inherent high surface "tack" which such polymeric foam layers exhibit. This high surface tack characteristic causes the outer foam surfaces of the composite sheet to stick together when brought into pressure contact during manufacture and storage, and also when the surfaces are brought into pressure contact during use. Such a characteristic, known as surface blocking, causes delamination of the foam layers from the reinforcing fabric, and therefore does not result in a commercially feasible product. Attempts to reduce surface tack by chemical modification of the polymeric foam compositions, as by cross-linking the polymeric components to a greater extent, generally lowers the surface tack, but correspondingly detracts from the desired soft drapeable natural chamois appearance, and also significantly reduces the liquid absorption and retention capabilities of the product.